With regard to fast circuits, there is increasing interest directed towards silicon or silicon-germanium MOSFETs having a short channel length. Switching times in the region of 10 ps can be achieved with silicon short-channel MOS transistors having channel lengths of less than 100 nm. The channel length is in this case given by the dimension of the gate electrode minus gate-source and gate-drain overlap.
IBM TDB Volume 33, June 1990, pages 75 to 77 discloses structuring the gate electrode for a short-channel transistor using a spacer as an etching mask.
Furthermore, it is known (see, for example, U.S. Pat. No. 5 231 038 and German Reference DE 42 34 777 A1) to reduce the structure size, which determines the channel length, of the gate electrode at the surface of the channel by producing the gate electrode with a T-shaped cross-section. For this purpose, insulating spacers are formed on flanks, which face the channel region, of connections of the source/drain regions, above which spacers the gate electrode is formed. The gate electrode laterally overlaps the insulating spacers in the upper region. As an alternative (see German Reference DE 42 34 777 A1), the gate electrode is formed from two different metal layers. Following the structuring of the upper metal layer, the lower metal layer is etched back below the lateral dimensions of the upper metal layer.
At switching speeds of this type, the RC constants of the gate electrodes are no longer negligible. In addition, the resistance of the gate electrode, which is usually composed of polysilicon, which is doped and possibly silicide-treated or coated with other materials of better conductivity, rises with shorter edge length, which is attributed, for example, to grain boundary influences.